This invention relates to an image display apparatus which employs a cathode ray tube and a method of correcting an image displayed on an image display apparatus which employs a cathode ray tube against an inclination caused by the terrestrial magnetism.
Generally, an image display apparatus which employs a cathode ray tube such as a television receiver is influenced by a magnetic field of the terrestrial magnetism or the like depending upon the place or the direction at or in which it is placed such that the image on the screen of the cathode ray tube is displaced upwardly or downwardly or is inclined or rotated.
Particularly, television broadcasting at present provides an image principally of the aspect ratio of 4:3, and when a television broadcast of the aspect ratio of 4:3 is received by a wide television receiver of another aspect ratio of 16:9 and the image of the television broadcast is expanded horizontally so that it is displayed as a wide image on the wide television receiver, the image suffers from noticeable displacement in a rotational direction by a magnetic field provided by the terrestrial magnetism.
Conventionally, in such an image display apparatus which employs a cathode ray tube as described above, correction current is supplied to a terrestrial magnetism correction coil provided at a boundary location between a funnel portion and a neck portion of the cathode ray tube to correct the image on the screen of the cathode ray tube so that it may not suffer from an inclination caused by the magnetic field of the terrestrial magnetism, that is, from being displaced upwardly or downwardly or from being rotated.
Conventionally, however, the inclination of the image is adjusted while a reference video of a television broadcast being broadcast at present for allowing correction of the image against an inclination caused by the terrestrial magnetism is displayed on the screen of the cathode ray tube of the television receiver. Therefore, good correction current cannot be obtained until it is waited that the reference video is displayed. Consequently, there is a disadvantage that much time is required for adjustment to obtain good correction current.
The adjustment for obtaining correction current is performed with reference to a portion of the video being broadcast which is considered to be horizontal. This is disadvantageous in that it is difficult to obtain optimum correction current.
It is an object of the present invention to provide an image display apparatus employing a cathode ray tube and an image correction method for the image display apparatus by which appropriate correction current used for correction of an image on the cathode ray tube against an inclination caused by the terrestrial magnetism can be obtained in a short time.
In order to attain the object described above, according to an aspect of the present invention, there is provided an image display apparatus which employs a cathode ray tube, comprising means for issuing a correction instruction to correct an image displayed on a screen of the cathode ray tube against an inclination and/or a vertical displacement caused by the terrestrial magnetism, and means operable in response to the correction instruction for causing a reference for correction to be displayed on the screen of the cathode ray tube.
With the image display apparatus, when a display image is to be corrected against an inclination caused by the terrestrial magnetism, the reference for correction is displayed on the screen of the cathode ray tube, and the display image is corrected against the inclination caused by the terrestrial magnetism with reference to the display of the reference for correction by the user. Consequently, the image display apparatus is advantageous in that the user can obtain correction current with which the display image can be corrected appropriately against the inclination caused by the terrestrial magnetism in a short time.
Preferably, the means operable in response to the correction instruction causes the image on the screen of the cathode ray tube to be adjusted so that the image is displayed entirely with a uniform compression ratio. With the image display apparatus, when the display image is to be corrected against the inclination caused by the terrestrial magnetism, it is displayed entirely with a uniform compression ratio. Consequently, the correction of the image can be performed under the uniform condition and good correction of the image against the inclination can be achieved.
According to another aspect of the present invention, there is provided a method of correcting an image displayed on an image display apparatus which employs a cathode ray tube against an inclination and/or a vertical displacement caused by the terrestrial magnetism, comprising the steps of displaying, in response to a correction instruction to correct the image against an inclination and/or a vertical displacement caused by the terrestrial magnetism, a reference for correction on the screen of the cathode ray tube, and correcting the image against the inclination and/or the vertical displacement caused by the terrestrial magnetism with reference to the display of the reference for correction.
With the method of correcting an image displayed on the image display apparatus, when a display image is to be corrected against an inclination caused by the terrestrial magnetism, the reference for correction is displayed on the screen of the cathode ray tube first, and then the display image is corrected against the inclination caused by the terrestrial magnetism with reference to the display of the reference for correction by the user. Consequently, the user can obtain correction current with which the display image can be corrected appropriately against the inclination caused by the terrestrial magnetism in a short time.
Preferably, the correction of the image against the inclination and/or the vertical displacement caused by the terrestrial magnetism is performed after an image size on the screen of the cathode ray tube is adjusted so that the image is displayed entirely with a uniform compression ratio. With the method of correcting an image displayed on the image display apparatus, when the display image is to be corrected against the inclination caused by the terrestrial magnetism, it is displayed entirely with a uniform compression ratio. Consequently, the correction of the image can be performed under the uniform condition and good correction of the image against the inclination can be achieved.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.